Push-to-connect tube couplings heretofore have been provided to allow for quick connection and sealing of a tube to the coupling simply by inserting the tube into the coupling. One such push-to-connect tube coupling is described in U.S. Pat. No. 4,063,760. Here a coupling nut is screwed onto the threaded portion of a tubular body having a forward threaded end for connection to another device. A radially expandable lock ring is provided in a chamber in the coupling nut, and the lock ring when in a relaxed condition has an inner diameter less than the outer diameter of the push-in tube. The push-in tube has locking sleeve that is provided with a camming ramp that terminates as a locking surface. When the push-in tube is pushed through the coupling nut and into the tubular body, the camming ramp radially outwardly expands the lock ring into the chamber in the coupling nut to allow passage of the push-in tube. During further pushing of the push-in tube the expanded lock ring slips over the case, until the lock ring passes behind the locking surface thereby securely to fix the push-in tube in the tubular body by the screwed-on coupling nut. The sealing of this fitting is done via a seal inserted in an annular recess at the inside of the tubular body, which seal closely receives the end portion of the push-in tube in a region thereof that extends beyond the locking sleeve.
The tubular body of the '760 patent must be specially fabricated for use in the described manner. In particular, the inner diameter of the tubular body must be turned at its inner diameter to form the annular groove that contains the annular seal that seals around the end of the push-in tube. The position of the seal also makes it somewhat difficult to install the annular seal or replace a worn annular seal as may be needed during the life of the coupling.